SortingIterator Class Reference

An adapter that takes in another RowIterator and produces the same rows, just in sorted order. More...

#include <sorting_iterator.h>

Inheritance diagram for SortingIterator:

Classes
union	IteratorHolder

Public Member Functions
	SortingIterator (THD *thd, Filesort *filesort, unique_ptr_destroy_only< RowIterator > source, ha_rows num_rows_estimate, table_map tables_to_get_rowid_for, ha_rows *examined_rows)
	~SortingIterator () override
bool	Init () override
	Initialize or reinitialize the iterator. More...
int	Read () override
	Read a single row. More...
void	SetNullRowFlag (bool is_null_row) override
	Mark the current row buffer as containing a NULL row or not, so that if you read from it and the flag is true, you'll get only NULLs no matter what is actually in the buffer (typically some old leftover row). More...
void	UnlockRow () override
void	CleanupAfterQuery ()
	Optional (when JOIN::destroy() runs, the iterator and its buffers will be cleaned up anyway); used to clean up the buffers a little bit earlier. More...
const Filesort *	filesort () const
Public Member Functions inherited from RowIterator
	RowIterator (THD *thd)
virtual	~RowIterator ()=default
	RowIterator (const RowIterator &)=delete
	RowIterator (RowIterator &&)=default
virtual const IteratorProfiler *	GetProfiler () const
	Get profiling data for this iterator (for 'EXPLAIN ANALYZE'). More...
virtual void	SetOverrideProfiler ([[maybe_unused]] const IteratorProfiler *profiler)
virtual void	StartPSIBatchMode ()
	Start performance schema batch mode, if supported (otherwise ignored). More...
virtual void	EndPSIBatchModeIfStarted ()
	Ends performance schema batch mode, if started. More...
virtual RowIterator *	real_iterator ()
	If this iterator is wrapping a different iterator (e.g. More...
virtual const RowIterator *	real_iterator () const

Private Member Functions
int	DoSort ()
void	ReleaseBuffers ()

Private Attributes
Filesort *	m_filesort
unique_ptr_destroy_only< RowIterator >	m_source_iterator
unique_ptr_destroy_only< RowIterator >	m_result_iterator
Filesort_info	m_fs_info
Sort_result	m_sort_result
const ha_rows	m_num_rows_estimate
const table_map	m_tables_to_get_rowid_for
ha_rows *	m_examined_rows
union SortingIterator::IteratorHolder	m_result_iterator_holder

Additional Inherited Members
Protected Member Functions inherited from RowIterator
THD *	thd () const

Detailed Description

An adapter that takes in another RowIterator and produces the same rows, just in sorted order.

(The actual sort happens in Init().) Unfortunately, it is still bound to working off a TABLE object, which means that you can't use it to e.g. sort the output of a join without materializing into a temporary table first (ignoring that we currently have no Iterators for joins).

The primary reason for this is that we currently have no way of communicating read sets through Iterators, and SortingIterator needs to add fields used in ORDER BY to the read set for the appropriate tables. This could be mitigated by e.g. sending in an unordered_set<Field *>, but we don't currently have such a mechanism.

Constructor & Destructor Documentation

SortingIterator()

SortingIterator::SortingIterator	(	THD *	thd,
		Filesort *	filesort,
		unique_ptr_destroy_only< RowIterator >	source,
		ha_rows	num_rows_estimate,
		table_map	tables_to_get_rowid_for,
		ha_rows *	examined_rows
	)

~SortingIterator()

SortingIterator::~SortingIterator ( )

override

Member Function Documentation

CleanupAfterQuery()

void SortingIterator::CleanupAfterQuery

(

)

Optional (when JOIN::destroy() runs, the iterator and its buffers will be cleaned up anyway); used to clean up the buffers a little bit earlier.

When we get cached JOIN objects (prepare/optimize once) that can live for a long time between queries, calling this will become more important.

DoSort()

int SortingIterator::DoSort ( )

private

filesort()

const Filesort * SortingIterator::filesort ( ) const

inline

Init()

bool SortingIterator::Init ( )

overridevirtual

Initialize or reinitialize the iterator.

You must always call Init() before trying a Read() (but Init() does not imply Read()).

You can call Init() multiple times; subsequent calls will rewind the iterator (or reposition it, depending on whether the iterator takes in e.g. a Index_lookup) and allow you to read the records anew.

Implements RowIterator.

Read()

int SortingIterator::Read ( )

inlineoverridevirtual

Read a single row.

The row data is not actually returned from the function; it is put in the table's (or tables', in case of a join) record buffer, ie., table->records[0].

Return values

0	OK
-1	End of records
1	Error

Implements RowIterator.

ReleaseBuffers()

void SortingIterator::ReleaseBuffers ( )

private

SetNullRowFlag()

void SortingIterator::SetNullRowFlag ( bool  is_null_row )

overridevirtual

Mark the current row buffer as containing a NULL row or not, so that if you read from it and the flag is true, you'll get only NULLs no matter what is actually in the buffer (typically some old leftover row).

This is used for outer joins, when an iterator hasn't produced any rows and we need to produce a NULL-complemented row. Init() or Read() won't necessarily reset this flag, so if you ever set is to true, make sure to also set it to false when needed.

Note that this can be called without Init() having been called first. For example, NestedLoopIterator can hit EOF immediately on the outer iterator, which means the inner iterator doesn't get an Init() call, but will still forward SetNullRowFlag to both inner and outer iterators.

TODO: We shouldn't need this. See the comments on AggregateIterator for a bit more discussion on abstracting out a row interface.

Implements RowIterator.

UnlockRow()

void SortingIterator::UnlockRow ( )

inlineoverridevirtual

Implements RowIterator.

Member Data Documentation

m_examined_rows

ha_rows* SortingIterator::m_examined_rows

private

m_filesort

Filesort* SortingIterator::m_filesort

private

m_fs_info

Filesort_info SortingIterator::m_fs_info

private

m_num_rows_estimate

const ha_rows SortingIterator::m_num_rows_estimate

private

m_result_iterator

unique_ptr_destroy_only<RowIterator> SortingIterator::m_result_iterator

private

m_result_iterator_holder

union SortingIterator::IteratorHolder SortingIterator::m_result_iterator_holder

private

m_sort_result

Sort_result SortingIterator::m_sort_result

private

m_source_iterator

unique_ptr_destroy_only<RowIterator> SortingIterator::m_source_iterator

private

m_tables_to_get_rowid_for

const table_map SortingIterator::m_tables_to_get_rowid_for

private

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The documentation for this class was generated from the following files:

• sql/iterators/sorting_iterator.h
• sql/iterators/sorting_iterator.cc